This invention relates to the cleaning of ink jet print head apparatus having multiple orifices.
Many different types of digitally controlled printing systems of ink jet printing apparatus are presently being used. These ink jet printers use a variety of actuation mechanisms, a variety of marking materials, and a variety of recording media. For home applications, digital ink jet printing apparatus is the printing system of choice because low hardware cost makes the printer affordable to every one. Another application for digital inkjet printing uses large format printers. It is a further requirement that these large format printers provide low cost copies with an ever improving quality. Ink jet printing technology is the first choice in today""s art. Thus, there is a need for improved ways to make digitally controlled graphic arts media, such as billboards, large displays, and home photos for example, so that quality color images may be made at a high-speed and low cost, using standard or special paper.
Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because of its nonimpact, low-noise characteristics, its use of papers from plain paper to specialized high gloss papers and its avoidance of toner transfers and fixing. Inkjet printing mechanisms can be categorized as either continuous inkjet or droplet on demand ink jet. Continuous inkjet printing dates back to at least 1929. See U.S. Pat. No. 1,941,001 to Hansell.
U.S. Pat. No. 3,373,437, issued to Sweet et al. in 1967, discloses an array of continuous inkjet orifices wherein ink droplets to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection continuous inkjet, and is used by several manufacturers, including Elmjet and Scitex.
U.S. Pat. No. 3,416,153, issued to Hertz et al. in 1966, discloses a method of achieving variable optical density of printed spots in continuous inkjet printing using the electrostatic dispersion of a charged droplet stream to modulate the number of droplets which pass through a small orifice. This technique is used in ink jet printers manufactured by Iris.
U.S. Pat. No. 3,878,519, issued to Eaton in 1974, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates.
U.S. Pat. No. 4,346,387, issued to Hertz in 1982 discloses a method and apparatus for controlling the electric charge on droplets formed by the breaking up of a pressurized liquid stream at a droplet formation point located within the electric field having an electric potential gradient. Droplet formation is effected at a point in the field corresponding to the desired predetermined charge to be placed on the droplets at the point of their formation. In addition to charging tunnels, deflection plates are used to actually deflect droplets.
Conventional continuous ink jet utilizes electrostatic charging tunnels that are placed close to the point where the droplets are formed in a stream. In this manner individual droplets may be charged. The charged droplets may be deflected downstream by the presence of deflector plates that have a large potential difference between them. A gutter (sometimes referred to as a xe2x80x9ccatcherxe2x80x9d) may be used to intercept the charged droplets, while the uncharged droplets are free to strike the recording medium. If there is no electric field present or if the break off point from the droplet is sufficiently far from the electric field (even if a portion of the stream before droplets break off is in the presence of an electric field), then charging will not occur.
The on demand type inkjet printers are covered by hundreds of patents and describe two techniques for droplet formation. At every orifice, (about 30 to 200 are used for a consumer type printer) a pressurization actuator is used to produce the ink jet droplet. The two types of actuators are heat and piezo materials. The heater at a convenient location heats ink and a quantity will phase change into a gaseous steam bubble and raise the internal ink pressure sufficiently for an ink droplet to be expelled to a suitable receiver. The piezo ink actuator incorporates a piezo material. It is said to possess piezo electric properties if an electric charge is produced when a mechanical stress is applied. This is commonly referred to as the xe2x80x9cgenerator effectxe2x80x9d. xe2x80x9cThe converse also holds true; an applied electric field will produce a mechanical stress in the material. This is commonly referred to as the xe2x80x9cmotor effectxe2x80x9d. Some naturally occurring materials possessing these characteristics are quartz and tourmaline. Some artificially produced piezoelectric crystals are: Rochelle salt, ammonium dihydrogen phosphate (ADP) and lithium sulphate (LH). The class of materials used for piezo actuators in an ink jet print head possessing those properties includes polarized piezoelectric ceramics. They are typically referred to as ferroelectric materials. In contrast to the naturally occurring piezoelectric crystals, ferroelectric ceramics are of the xe2x80x9cpolycrystallinexe2x80x9d structure. The most commonly produced piezoelectric ceramics are: lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate. For the ink jet print head a ferroelectric ceramic is machined to produce ink chambers. The chamber is water proofed by gold plating and becomes a conductor to apply the charge and cause the piezo xe2x80x9cmotor effectxe2x80x9d. This xe2x80x9cmotor effectxe2x80x9d causes the ink cavity to shrink, raise the internal pressure, and generate an ink droplet.
Inks for high speed jet droplet printers must have a number of special characteristics. Typically, water-based inks have been used because of their conductivity and viscosity range. Thus, for use in a jet droplet printer the ink must be electrically conductive, having a resistivity below about 5000 ohm-cm and preferably below about 500 ohm-cm. For good flow through small orifices water-based inks generally have a viscosity in the range between about 1 to 15 centipoise at 25 degree C.
Over and above this, the ink must be stable over a long period of time, compatible with the materials comprising the orifice plate and ink manifold, free of living organisms, and functional after printing. The required functional characteristics after printing are: smear resistance after printing, fast drying on paper and waterproof when dry. Examples of different types of water-based jet droplet printing inks are found in U.S. Pat. Nos. 3,903,034; 3,889,269; 3,870,528; 3,846,141; 3,776,642; and 3,705,043.
The ink also has to incorporate a nondrying characteristic in the jet cavity so that the drying of ink in the cavity is hindered or slowed to such a degree that through occasional spitting of ink droplets the cavities can be kept open. The addition of glycol will facilitate the free flow of ink through the ink jet. Ink jet printing apparatus typically includes an ink jet print head that is exposed to the various environments where ink jet printing is utilized. The orifices are exposed to all kinds of air born particles. Particulate debris accumulates on the surfaces, forming around the orifices. The ink will combine with such particulate debris to form an interference burr to block the orifice or cause through an altered surface wetting to inhibit a proper formation of the ink droplet. That particulate debris has to be cleaned from the orifice to restore proper droplet formation. This cleaning commonly is achieved by wiping, spraying, vacuum suction, and/or spitting of ink through the orifice. The wiping is the most common application.
Inks used in ink jet printers can be said to have the following problems:
1) they require a large amount of energy to dry after printing;
2) large printed areas on paper usually cockle because of the amount of water present;
3) the printed images are sensitive to wet and dry rub;
4) the compositions of the ink usually require an anti-bacterial preservative to minimize the growth of bacteria in the ink;
5) the inks tend to dry out in and around the orifices resulting in clogging;
6) the wiping of the orifice plate causes wear on plate and wiper;
7) the wiper itself generates particles that clog the orifice;
8) cleaning cycles are time consuming and slow the productivity of ink jet printers. It is especially of concern in large format printers where frequent cleaning cycles interrupt the printing of an image; and
9) when a special printing pattern is initiated to compensate for plugged or badly performing orifices, the printing rate declines.
Some of these problems may be overcome by the use of polar, conductive organic solvent based ink formulations. However, the use of non-polar organic solvents is generally precluded by their lack of electrical conductivity. The addition of solvent soluble salts can make such inks conductive, but such salts are often toxic, corrosive, and unstable.
These objects are achieved by an ink jet printer having an ink jet printer having a printhead defining a plurality of orifices for ejecting ink droplets. The printer comprises a source of cleaning fluid, a cleaning member having a surface partially dipped in the cleaning fluid, a first drive mechanism to move the cleaning member surface creating a flow of cleaning fluid on the surface and a second drive mechanism to advance the printhead and the cleaning member surface into a proximate and separate relation with the cleaning member surface wherein at least one of the orifices of the printhead enters the flow of cleaning fluid wherein the print head and the cleaning member surface are separated by gap of between 0.1 mm and 2.54 mm.
According to another aspect of the present invention, these objects of the invention are achieved by an inkjet printer having a printhead with a structure defining at least one ink drop ejection orifice and a liquid collection vessel adapted to contain a cleaning fluid. A roller is partially submerged in the cleaning fluid and a first actuator fixed to and rotating the roller to create a continuous flow of cleaning fluid about the roller. A second actuator variably positions the roller and the printhead between two separated positions, a distal position and a proximate position wherein at least one orifice of the printhead enters into the flow of cleaning fluid.
According to another aspect the objects of the present invention are met by an ink jet printer comprising a printhead defining at least one orifice for ejecting ink droplets and a source of cleaning fluid. A cleaning member having a surface is partially dipped in the cleaning fluid. A first drive mechanism is provided to move the cleaning member surface creating a flow of cleaning fluid on the surface and a second drive mechanism is provided to advance the printhead and the cleaning member surface into a proximate and separate relation with the cleaning member surface wherein at least one orifice of the printhead enters the flow of cleaning fluid. A computer operates the first drive mechanism and second drive mechanism to clean the print head using at least a normal cleaning mode and a high cleaning mode wherein the computer detects conditions indicating the extent of cleaning needed by the print head and changes cleaning modes based upon detected conditions.
Rapid cleaning of orifices in accordance with the present invention can be accomplished in such a short time because of the efficiency of cleaning apparatus in accordance with the present invention.
The cleaning fluid on the roller is replenished at a predetermined rate and removes waste ink and particulate debris permanently from the inkjet print head.
Another advantage of this invention is that the cleaning fluid on the roller can have a substantial thickness thereby minimizing the requirements for mechanical tolerances.
Another advantage of this cleaning technique is that with no mechanical rubbing, the wear of the delicate orifice plate is eliminated or greatly reduced. The replacement of the ink jet head will be less frequent and more of the orifices will stay functional to result in a higher image quality.
Another advantage is that individual inks can be cleaned by selecting the rotation rate of the roller to change the turbulence or agitation rate. In this way, the speed of the roller can be selected to match the cleaning needs of a particular ink. In other words, red, green, and blue inks in the same cartridge can have different roller speeds.